An attack by loansharks has emerged as a possible cause of Wednesday's fire in Kwun Tong which killed four people.

Residents said a barber shop and a clinic on the first floor of the On Hing Building had been vandalised by debt collectors a couple of months ago, and said threats had been daubed on corridor walls.

Kowloon East police regional crime unit officers returned to the scene yesterday to collect evidence.

Detectives said they had heard about the claims and were investigating them.

Police said they had not ruled out the possibility of arson.

Fifth-floor resident Wong Yue-hing said: 'The barber shop seems to have been involved in financial troubles. There had been vandal attacks one or two months ago.

'I heard it was a loanshark. I am not sure if they had reported the case to police.' Police yesterday took eight blackened fire extinguishers from the block. Officers said they wanted to establish whether the extinguishers had been in working order and, if not, whether they had been deliberately damaged.

The fire broke out before dawn on Wednesday near an electrical switch box on the first floor.

Smoke quickly engulfed the corridors and four people died as they tried to escape.

Firemen are puzzled by the high number of casualties, as the blaze did not generate many flames and firefighters arrived three minutes after receiving the first report.

Poor fire safety management has been blamed in part for the death toll.

Some smoke doors were broken while others had been wedged open. The fire exit was said to have been locked.

Buildings Department inspectors yesterday said huts on the roof of the building were illegal structures.

The Lands Department said the barber shop and clinic on the first floor were illegal conversions.

The eight-storey block was reopened last night to allow residents to collect their valuables.

Meanwhile, fire services inspectors yesterday conducted a surprise blitz at several nearby blocks feared to be fire hazards. The blocks were last checked three months ago but officers found little improvement had been made. Warning letters were issued telling residents to clear blocked smoke doors and unlock fire exits.